Existing two-dimensional portable bar code readers employ a mechanically scanned laser beam. In one type of such reader, the beam is mechanically scanned horizontally as in conventional, one dimensional bar code scanners, while it is also manually scanned vertically with a downward motion of the hand or wrist. In a more sophisticated type of two-dimensional reader, the laser beam is mechanically scanned in both the horizontal and vertical directions utilizing a raster.
These laser readers require that the scanning beam pattern be accurately aligned with the label symbology, with the degree of accuracy being a function of the vertical height of the coding elements versus the horizontal width. Further, reading the two dimensional codes line by line requires stitching separately read lines or words after they are read. Some two dimensional codes (portable data files and the like) do not provide for stitching. A further limitation of laser scanners for two-dimensional reading is that they require a significant amount of time for the label to be read, which of course requires that the scanner remain accurately aligned with the label throughout the reading process.